There is no antonym for the concept of fabric.
There are many, many materials that are not fabric, and there are even more that are not materials. For each of the properties of fabric, there are things that do not have that property. Each of these has its own name, but there is not a name for all the things that are not fabric.
There are many, many materials that are not fabric, and there are even more that are not materials. For each of the properties of fabric, there are things that do not have that property. Each of these has its own name, but there is not a name for all the things that are not fabric.